There are various types of capacitor used in electronics. Among all, aluminum electrolytic capacitors are preferred to be connected to a power line of a semiconductor device, such as a central processing unit (CPU) and large scale integration (LSI), taking advantage of the high capacity and to be implemented in an on-board substrate as a capacitor for compensation for momentary voltage drop.
Such an aluminum electrolytic capacitor is fabricated by rolling separators into an anode foil and a cathode foil that have aluminum as a material and connecting conductor bars for electrically drawing each electrode to outside to the anode foil and the cathode foil, respectively. In order to avoid creating contact potential difference against the anode foil or the cathode foil, it is preferred to use aluminum for a material of the conductor bars that is a material same as the material of the anode foil and the cathode foil.
Then, an end of such conductor bar is connected to a lead for implementation of the aluminum electrolytic capacitor in a circuit board. As the lead, in order to electrically connect the aluminum electrolytic capacitor to the circuit board in a good condition, a copper wire or a copper-clad steel wire with low electrical resistance is used. The aluminum electrolytic capacitor is soldered to the circuit board while, for good solder wettability, the surface of the copper wire is covered with a tin layer in advance.
Here, to connect the leads to the above conductor bars, electric welding that is easy to connect is used. Upon such electric welding, the tin layer on the surface of the lead is melted to be reattached to the surface of the welded portion and thus a tin layer of uncertain thickness is formed in the welded portion of the lead and the conductor bar. Mechanical stress is inherent in the tin layer, and it is understood that a plating whisker, called as a whisker, grows on the surface of the tin layer caused by the stress.
Examples of related art are Japanese Laid-open Patent Publication Nos. 2003-272963, 2007-67146, 2008-130782, 2008-108865, 2009-212175, 2010-153712, 2010-153713, 2010-161277, 2008-235322, and 2010-3811 and International Publication Pamphlet No. WO 2007/043181.